Switching display update properties upon detecting a power management event

ABSTRACT

Systems and methods provide automatic switching of display update properties such as screen resolution, pixel depth, and refresh rate in response to a power management event. The display update property may be decreased when power is switched from AC power to DC power, for example, when the system is unplugged from a wall outlet and is running on battery power.

RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.10/677,146 filed Sep. 30, 2003 now U.S. Pat. No. 7,538,762 which isincorporated herein by reference in its entirety.

FIELD

The present invention relates generally to computer devices, and moreparticularly to switching display update properties such as screenresolution, pixel depth and refresh rates on such devices upon detectinga power management event.

COPYRIGHT NOTICE/PERMISSION

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever. The following notice applies to the software and dataas described below and in the drawings hereto: Copyright © 2003, IntelCorporation. All Rights Reserved.

BACKGROUND

Mobile computing systems such as laptop computers, notebook computers,PDAs (Personal Digital Assistants) and the like are becoming more andmore popular. A critical aspect of such systems is that they typicallyrun using battery power when they are not or cannot be connected to anAC power source. As a result, mobile computers typically provide powermanagement capabilities in order to run as long as possible off ofbattery power.

Various components on computing systems consume power. For example, avideo display (typically an LCD on mobile computing systems) and memoryassociated with video display consume power. The video display must becontinually refreshed, typically by a graphics engine on a graphicscontroller. The display is refreshed pixel by pixel, with the graphicsengine fetching the pixel data from memory. The act of fetching dataconsumes power on the graphics engine (or controller), the memorysubsystem containing the pixel data, and the display device itself.Typically the amount of power consumed is related to the refresh rateand the amount of memory required to support the video display. This inturn is related to the screen resolution. For example, a higher screenresolution will require more memory, and consequently more memory accessresulting in more power consumption with each refresh than a lowerresolution setting. Thus while high resolution screens on today's mobilecomputing devices provide increased image quality, they also consumemore power resulting in potentially short battery life.

In view of the above, there is a need in the art for the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an overview of a hardwareenvironment incorporating embodiments of the invention.

FIG. 2 is a block diagram providing details software environmentincorporating embodiments of the invention.

FIGS. 3A and 3B are flowcharts illustrating methods for dynamicallyswitching screen resolution upon receiving a power management eventaccording to embodiments of the invention.

DETAILED DESCRIPTION

In the following detailed description of exemplary embodiments of theinvention, reference is made to the accompanying drawings that form apart hereof, and in which is shown by way of illustration specificexemplary embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the various embodiments of the invention, and itis to be understood that other embodiments may be utilized and thatlogical, mechanical, electrical and other changes may be made withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense.

In the Figures, the same reference number is used throughout to refer toan identical component which appears in multiple Figures. Signals andconnections may be referred to by the same reference number or label,and the actual meaning will be clear from its use in the context of thedescription.

The detailed description is divided into multiple sections. In the firstsection the hardware and software operating environment of differentembodiments of the invention are described. In the second sectionmethods according to various embodiments of the invention are described.

Operating Environment

FIG. 1 is a block diagram of the major components of a hardwareenvironment 100 incorporating various embodiments of the invention. Ingeneral, the systems and methods of the various embodiments of theinvention may be incorporated on any hardware system supporting multiplepower sources, for example AC power source 130 and DC power source 132.Examples of such hardware includes laptop computers, portable handheldcomputers, personal digital assistants (PDAs), network enabled cellulartelephones, and hybrids of the aforementioned devices. In someembodiments of the invention, hardware environment 100 comprises aprocessor 102, a graphics and memory controller 104, memory 106 andvideo output 108. Communications between the processor and integratedgraphics and memory controller 104 occurs via processor system bus 120in some embodiments of the invention. In particular embodiments,processor system bus 120 is a 400-MHz source-synchronous front side bus.

Processor 102 may be any type of computational circuit such as, but notlimited to, a microprocessor, a complex instruction set computing (CISC)microprocessor, a reduced instruction set computing (RISC)microprocessor, a very long instruction word (VLIW) microprocessor, agraphics processor, a digital signal processor (DSP), or any other typeof processor, processing circuit, execution unit, or computationalmachine. In some embodiments of the invention, processor 102 may be aprocessor in the Pentium® or Celeron® family of processors availablefrom Intel Corporation, Santa Clara, Calif. Although only one processor102 is shown, multiple processors may be connected to system bus 120.

Graphics and memory controller 104 may provide graphics and videofunctions and may interface one or more memory devices to the processorsystem bus 120. In some embodiments, graphics and memory controller 104may be integrated on a single chip and may include graphics controller104.1 and memory controller 104.2. In alternative embodiments, graphicscontroller 104.1 may reside on a separate chip or chipset from memorycontroller 104.2. In further alternative embodiments, graphicscontroller 104.1 may reside on a video controller card (not shown).Graphics controller 104.1 may include various graphics sub-portions suchas a 3-dimensional (3D) engine, 2-dimensional (2D) engine, video engine,etc.

Graphics controller 104.1 may provide video output 108. Video output 108may be an interface to an LCD (Liquid Crystal Display) that is integralto a mobile computing environment in which system 100 resides, or videooutput may be an interface to an external display. In some embodiments,the interface to the LCD may be a LVDS (Low Voltage Differential Signal)interface. Additionally, video output 108 may be a Digital Video OutPort (DVOB or DVOC) or a CRT interface such as a VGA interface.

Memory controller 104.2 may interface with a system memory 106. Systemmemory 106 may be any type of volatile or non-volatile memory, includingany type of RAM (Random Access Memory), ROM (Read-Only Memory), flashmemory etc. In some embodiments, memory 106 may comprise DDR-SDRAM(Double Data Rate-Synchronous Dynamic Random Access Memory), a type ofSDRAM that supports data transfers on both edges of each clock cycle(the rising and falling edges), effectively doubling the memory chip'sdata throughput. DDR-SDRAM typically consumes less power, which makes itwell-suited to mobile computing environments.

In some embodiments, frame buffer 110 is part of system memory 106.Frame buffer 110 may be memory that stores pixel values for pixels on amonitor connected to video output 108, such as an integral LCD monitor.The amount of memory required for frame buffer 110 typically depends onthe pixel depth (e.g. the number of bits used for each color), thescreen width and the screen height. In alternative embodiments, framebuffer 110 may be a separate memory 110′ from system memory 106. Infurther alternative embodiments, frame buffer 110 may reside on agraphics controller card.

FIG. 2 illustrates an exemplary software environment 200 according tovarious embodiments of the invention. In some embodiments, softwareenvironment 200 includes operating system 202, video driver 204, powermanagement driver 206, BIOS (Basic Input/Output System) software 208,and power management user interface 210. Operating system 202 managesthe execution of programs and tasks running on processor 102, andmanages devices such as hard drives, floppy drives, CD-ROM drives,DVD-ROM drives, network interfaces and other devices. In someembodiments of the invention, operating system 202 may be one of theMicrosoft Windows family of operating systems available from MicrosoftCorporation of Redmond, Wash. These operating systems include Windows95®, Windows 98®, Windows CE®, Windows NT®, Windows 2000®, Windows ME®and Windows XP®. Additionally, operating system 202 may be a UNIXoperating system or a UNIX based operating system such as Linux® orFreeBSD. Alternatively, operating system 202 may be the Mac OS®operating system from Apple Computer Incorporated, Cupertino, Calif. Noembodiment of the invention is limited to a particular operating system.

Video driver 204 provides an interface between software such asoperating system 202 and applications controlled by operating system202, and video hardware such as graphics and memory controller 104.Video driver 204 typically translates standard operating system videofunctions for operating system 202 into the specific commands requiredby the specific video hardware and/or firmware resident on computersystem 100. These commands include commands that control the resolutionsetting, pixel depth setting and refresh rate for the video hardware.

In some embodiments, a power management driver 206 comprises softwarethat interfaces with power management hardware and firmware on computersystem 100. Examples of such functions include functions that detectwhether the computer system is currently connected to an AC powersource, functions that obtain the current state of a battery used toprovide power and functions that detect the level of charge in thebattery.

BIOS software 108 may reside in a separate memory from system memory106, and comprises a set of functions that control basic aspects ofhardware and hardware controllers that may be part of a computer system100. BIOS software 108 may also include functions that control theresolution of a video device, and may also include functions related topower management, such as the functions described above with respect topower management driver 206.

While some embodiments include BIOS software 108, not all embodimentsneed include or utilize BIOS software 108, and in alternativeembodiments the driver layer software such as video driver 204 and powermanagement driver 206 interface directly with the hardware rather thanthrough BIOS software 108.

Power management policies 212 comprise a set of one or more policiesthat define actions that take place upon the occurrence of powermanagement events. These polices may comprise default actions, or theymay be customized by a user through a power management user interface210. In some embodiments of the invention, the power management policiesinclude policies that define a screen resolution setting that is to beused upon the occurrence of particular power management events. Inalternative embodiments of the invention, the power management policiesinclude policies that define a pixel depth setting that is to be usedupon the occurrence of particular power management events. In furtheralternative embodiments, the power management policies include policiesthat define a refresh rate setting that is to be used upon theoccurrence of particular power management events. These power managementevents include switching the power source from AC (Alternating Current)to DC (Direct Current) and battery charge level events (e.g. a batteryreaching a certain percentage of charge or battery time remaining). Insome embodiments, power management user interface 210 may be provided aspart of a “control panel” interface, and provide various user interfacemechanisms (menus, buttons, icons etc.) for choosing and/or definingactions that are to take place upon power management events.

Methods

FIGS. 3A and 3B are flowcharts illustrating methods for automaticallyswitching display update properties upon the occurrence of powermanagement events according to embodiments of the invention. The methodsmay be performed within a hardware and software operating environmentsuch as that described above with reference to FIGS. 1 and 2. Themethods to be performed by the operating environment constitute computerprograms made up of computer-executable instructions. Describing themethods by reference to a flowchart enables one skilled in the art todevelop such programs including such instructions to carry out themethods on suitable computers (the processor of the computer executingthe instructions from computer-readable media such as RAM, ROM, CD-ROM,DVD-ROM, flash memory etc.). The methods illustrated in FIGS. 3A and 3Bare inclusive of the acts performed by an operating environmentexecuting an exemplary embodiment of the invention.

FIG. 3A illustrates a method 300 for dynamically switching displayupdate properties based on power management events. For the purposes ofthis specification, display update properties include screen resolutionsettings, pixel depth (i.e. the number of bits per pixel—also referredto as color quality) and refresh rate settings. In some embodiments, themethod begins when a system executing the method receives a powermanagement event (block 302). In some embodiments, the event mayindicate that a change has been made in the power source. For example,the event may indicate that the system is no longer connected to an ACpower source, or the event may indicate that the system has beenconnected to an AC power source. In embodiments where the operatingsystem is the Microsoft Windows based operating system, the event may bea “PBT_APMPOWERSTATUSCHANGE” event that is sent to one or moreapplications executing on the system.

A check is made to determine if a switch has been made from AC power toDC power, i.e. the system is now running on battery power (block 304).If so, the system may automatically decrease one or more display updateproperties (block 306). In some embodiments, the system decreases thescreen resolution (block 307). In alternative embodiments, the systemdecreases the pixel depth (block 308). In further alternativeembodiments, the system decreases the refresh rate (block 309). Thevarious embodiments of the invention may execute any combination of oneor more of blocks 307, 308 and 309. For example, if the screenresolution was set to a relatively high resolution, e.g. 1600×1200 or1280×1024, it may be reduced to 800×600 or 640×480. Similarly, if thepixel depth is 32 bits per pixel, the system may decrease the pixeldepth to 16 or 8 bits per pixel. Likewise, if the refresh rate is 60 Hz,it may be reduced to a value less than 60 Hz such as 50 Hz or 40 Hz. Theparticular refresh rate value chosen may depend on rates supported bythe graphics controller and display hardware. It should be noted thatthe invention is not limited to any particular decrease in screenresolution, pixel depth, or refresh rate. Further, it should be notedthat if the screen resolution or pixel depth is already at a relativelylow value then no decrease in the value may be required. Similarly, ifthe refresh rate was already at a relatively low refresh rate, nodecrease in refresh rate may be required.

In embodiments where the operating system is the Microsoft Windows basedoperating system, the system may execute a “GetSystemPowerStatus”function to determine the current power status of the system, and mayuse operating system functions to set the resolution.

Further, the system may check to determine if the event is generatedbecause a switch has been made from DC power to AC power, i.e. thesystem is now connected to an AC power source, and the battery may berecharging (block 310). If so, the system may automatically increase oneor more display update properties (block 312). In some embodiments, thesystem increases the screen resolution (block 314). In alternativeembodiments, the system increases the pixel depth (block 316). Infurther alternative embodiments, the system increases the refresh rate(block 318). The various embodiments of the invention may execute anycombination of one or more of blocks 314, 316 or 318. For example, ifthe screen resolution was set to a relatively low resolution, e.g.800×600 or 640×480, it may be increased to 1600×1200 or 1280×1024.Similarly, if the pixel depth is set to 16 bits per pixel, the systemmay increase the pixel depth to 32 bits per pixel. Likewise, if therefresh rate is 40 Hz or 50 Hz, it may be increased to a value of 60 Hzor above. Again, the particular refresh rate value chosen may depend onrates supported by the graphics controller and display hardware. Itshould be noted that the invention is not limited to any particularincrease in screen resolution, pixel depth or refresh rate. Further, itshould be noted that if the screen resolution or pixel depth is alreadyat a relatively high value that no increase may be necessary. Similarly,if the refresh rate is already at a relatively high rate, no increasemay be necessary.

The system then returns to block 302 to await the next power managementevent.

FIG. 3B illustrates a method 320 according to various embodiments of theinvention for policy based dynamic switching of screen resolution basedon power management events. In some embodiments, the method begins whena system executing the method receives a power management event (block302). In some embodiments, the event may indicate that a change has beenmade in the power source. For example, the event may indicate that thesystem is no longer connected to an AC power source, or the event mayindicate that the system has been connected to an AC power source. Inalternative embodiments, the event may include a battery power levelcrossing a predetermined threshold indicating the level of charge in thebattery. The predetermined threshold may be expressed as a percentage ofcharge left in the battery, or the threshold may be expressed in termsof time left until the battery is no longer able to provide sufficientpower to keep the system running.

Next, the system checks to determine if the power management eventmatches a predetermined power management policy defining a displayupdate property or properties (i.e. the screen resolution, pixel depthand/or refresh rate) for the event (block 322). The predetermined powermanagement policy may be a default policy, or it may be a policy definedby a user of the mobile computer system.

If there is a power management policy related to a display updateproperty or properties that match the event, then the system sets thedisplay update property or properties as defined by the policy (block324). Otherwise the system returns to block 302 to wait for the nextpower management event.

The tasks described with reference to FIGS. 3A and 3B above may beexecuted by an operating system, by software residing on a graphicscontroller, software running on a power management controller, or anycombination thereof. The embodiments of the invention are not limited toany particular distribution of functionality indicated in the method.

Systems and methods for automatically switching screen resolution upondetecting a power management event have been described. The embodimentsof the invention provide advantages over previous systems. For example,the systems and methods of the various embodiments of the inventionprovide a means for screen resolution, pixel depth and/or video refreshrate to be lowered upon detecting a switch from AC to DC power. Thelower screen resolution, pixel depth and/or refresh rate may provide adecrease in power consumption by the system. This in turn may extend thebattery life for a mobile computing system. Similarly, upon detecting aswitch from DC to AC power, the systems and methods of the variousembodiments of the invention may increase display update propertiesresulting in desirable image quality when the user need not worry aboutconsuming battery power.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations of the presentinvention.

The terminology used in this application is meant to include all ofthese environments. It is to be understood that the above description isintended to be illustrative, and not restrictive. Many other embodimentswill be apparent to those of skill in the art upon reviewing the abovedescription. Therefore, it is manifestly intended that this invention belimited only by the following claims and equivalents thereof.

1. An apparatus comprising: a power management driver executed by one ormore processors to receive an indication of a power situation; a videodriver executed by one or more processors to (1) select a policy from aplurality of power management policies, wherein the selected policy isresponsive to the power situation and (2) request to change a displayproperty of a video display based on the selected policy and wherein thedisplay property is at least one of a video color quality, screenresolution, and screen refresh rate; and video hardware to selectivelyadjust a display property in response to the request to change a displayproperty.
 2. The apparatus of claim 1, wherein the power situationcomprises a change in a power source from AC power to DC power andwherein the request to change a display property includes a request todecrease at least one of the video color quality, screen resolution, andscreen refresh rate.
 3. The apparatus of claim 1, wherein the powersituation comprises a change in a power source from DC power to AC powerand wherein the request to change an a display property includes arequest to increase at least one of the video color quality, screenresolution, and screen refresh rate.
 4. The apparatus of claim 1,wherein the power situation comprises a power level of a battery fallingbelow a predetermined threshold and wherein the request to change adisplay property includes a request to decrease at least one of thevideo color quality, screen resolution, and screen refresh rate.
 5. Theapparatus of claim 1, wherein the power situation comprises a powerlevel of a battery meeting or exceeding a predetermined threshold andwherein the request to change a display property includes a request toincrease at least one of the video color quality, screen resolution, andscreen refresh rate.
 6. A computer-implemented method of determining animage display property comprising: receiving a power situation;selecting a scheme from a plurality of power management schemes, whereinthe selected scheme is responsive to the power situation; changing animage display property in response to the power situation and inaccordance with the selected scheme, wherein the image display propertyis at least one of a color quality, screen resolution, and screenrefresh rate; and providing an image for display in accordance with theimage display property.
 7. The computer-implemented method of claim 6,wherein at least one power management scheme is selected by a user. 8.The computer-implemented method of claim 6, wherein the power situationcomprises a change in a power source from AC power to DC power andwherein changing an image display property includes decreasing at leastone of the video color quality, screen resolution, and screen refreshrate.
 9. The computer-implemented method of claim 6, wherein the powersituation comprises a change in a power source from DC power to AC powerand wherein changing an image display property includes increasing atleast one of the video color quality, screen resolution, and screenrefresh rate.
 10. The computer-implemented method of claim 6, whereinthe power situation comprises a power level of a battery falling below apredetermined threshold and wherein changing an image display propertyincludes decreasing at least one of the video color quality, screenresolution, and screen refresh rate.
 11. The computer-implemented methodof claim 6, wherein the power situation comprises a power level of abattery meeting or exceeding a predetermined threshold and whereinchanging an image display property includes increasing at least one ofthe video color quality, screen resolution, and screen refresh rate. 12.A computer-implemented method comprising: detecting a power managementevent; selecting a policy from a plurality of power management policies,wherein the selected policy is responsive to the power management event;changing a screen resolution in response to the power management event,wherein the screen resolution is changed in accordance with the selectedpolicy; and providing an image for display in accordance with thechanged screen resolution.
 13. The computer-implemented method of claim12, wherein the power management event comprises a change in a powersource from AC power to DC power and wherein changing a screenresolution includes decreasing screen resolution.
 14. Thecomputer-implemented method of claim 12, wherein the power managementevent comprises a change in a power source from DC power to AC power andwherein changing a screen resolution includes increasing screenresolution.
 15. The computer-implemented method of claim 12, wherein thepower management event comprises a power level of a battery fallingbelow a predetermined threshold and wherein changing screen resolutioncomprises decreasing screen resolution.
 16. The computer-implementedmethod of claim 12, wherein the power management event comprises a powerlevel of a battery meeting or exceeding a predetermined threshold andwherein changing screen resolution includes increasing screenresolution.
 17. A computer-implemented method of determining an imagedisplay property comprising: receiving a power situation; selecting apolicy from a plurality of power management policies, wherein theselected policy is responsive to the power situation; changing an imagedisplay property in response to the power situation and in accordancewith the selected policy, wherein the image display property isselectable as any one or more of a video color quality, screenresolution, and screen refresh rate; and providing an image for displayin accordance with the image display property.
 18. At least one computerreadable medium comprising instructions stored thereon, which whenexecuted by a computer cause the computer to: access a power situation;select a policy from a plurality of power management policies, whereinthe selected policy is responsive to the power situation; change animage display property in response to the power situation and inaccordance with the selected policy, wherein the image display propertyis at least one of a video color quality, screen resolution, and screenrefresh rate; and provide an image for display in accordance with theimage display property.
 19. The at least one computer-readable medium ofclaim 18, wherein the power situation is selected by a user.
 20. The atleast one computer-readable medium of claim 18, wherein at least onepower management policy is selected by a user.
 21. The at least onecomputer-readable medium of claim 18, further storing instructionsthereon, which when executed by a computer, cause the computer to:receive specification of at least one power management policy through apower management user interface.
 22. The at least one computer-readablemedium of claim 18, wherein the power situation comprises a change in apower source from AC power to DC power and wherein to change an imagedisplay property, the computer is to decrease at least one of the videocolor quality, screen resolution, and screen refresh rate.
 23. The atleast one computer-readable medium of claim 18, wherein the powersituation comprises a change in a power source from DC power to AC powerand wherein to change an image display property, the computer is toincrease at least one of the video color quality, screen resolution, andscreen refresh rate.
 24. The at least one computer-readable medium ofclaim 18, wherein the power situation comprises a power level of abattery falling below a predetermined threshold and wherein to change animage display property, the computer is to decrease at least one of thevideo color quality, screen resolution, and screen refresh rate.
 25. Theat least one computer-readable medium of claim 18, wherein the powersituation comprises a power level of a battery meeting or exceeding apredetermined threshold and wherein to change an image display property,the computer is to increase at least one of the video color quality,screen resolution, and screen refresh rate.
 26. At least one computerreadable medium comprising instructions stored thereon, which whenexecuted by a computer cause the computer to: detect a power managementevent; select a policy from a plurality of power management policies,wherein the selected policy is responsive to the power management event;change a screen resolution in response to the power management event,wherein the screen resolution is changed in accordance with the selectedpolicy; and cause display of an image in accordance with the changedscreen resolution.
 27. The at least one computer-readable medium ofclaim 26, wherein the power management event comprises a change in apower source from AC power to DC power and wherein to change a screenresolution, the computer is to decrease screen resolution.
 28. The atleast one computer-readable medium of claim 26, wherein the powermanagement event comprises a change in a power source from DC power toAC power and wherein to change a screen resolution, the computer is toincrease screen resolution.
 29. The at least one computer-readablemedium of claim 26, wherein the power management event comprises a powerlevel of a battery falling below a predetermined threshold and whereinto change a screen resolution, the computer is to decrease screenresolution.
 30. The at least one computer-readable medium of claim 26,wherein the power management event comprises a power level of a batterymeeting or exceeding a predetermined threshold and wherein to change ascreen resolution, the computer is to increase screen resolution.
 31. Anapparatus comprising: at least one processor configured to: detect apower management event; select a policy from a plurality of powermanagement policies, wherein the selected policy is responsive to thepower management event; change a screen resolution in response to thepower management event, wherein the screen resolution is changed inaccordance with the selected policy; and cause display of an image inaccordance with the changed screen resolution.
 32. The apparatus ofclaim 31, wherein the power management event comprises a change in apower source from AC power to DC power and wherein to change a screenresolution, the at least one processor is to decrease screen resolution.33. The apparatus of claim 31, wherein the power management eventcomprises a change in a power source from DC power to AC power andwherein to change a screen resolution, the at least one processor is toincrease screen resolution.
 34. The apparatus of claim 31, wherein thepower management event comprises a power level of a battery fallingbelow a predetermined threshold and wherein to change a screenresolution, the at least one processor is to decrease screen resolution.35. The apparatus of claim 31, wherein the power management eventcomprises a power level of a battery meeting or exceeding apredetermined threshold and wherein to change a screen resolution, theat least one processor is to increase screen resolution.
 36. Acomputer-implemented method of determining an image display propertycomprising: receiving a power situation; selecting a policy from aplurality of power management policies, wherein the selected policy isresponsive to the power situation; changing an image display property inresponse to the power situation and in accordance with the selectedpolicy, wherein the image display property is at least one of a videocolor quality, screen resolution, and screen refresh rate; and providingan image for display in accordance with the image display property. 37.The computer-implemented method of claim 36, wherein the power situationis selected by a user.
 38. The computer-implemented method of claim 36,wherein at least one power management policy is selected by a user. 39.The computer-implemented method of claim 36, further comprising:receiving specification of at least one power management policy througha power management user interface.
 40. The computer-implemented methodof claim 36, wherein the power situation comprises a change in a powersource from AC power to DC power and wherein changing an image displayproperty includes decreasing at least one of the video color quality,screen resolution, and screen refresh rate.
 41. The computer-implementedmethod of claim 36, wherein the power situation comprises a change in apower source from DC power to AC power and wherein changing an imagedisplay property includes increasing at least one of the video colorquality, screen resolution, and screen refresh rate.
 42. Thecomputer-implemented method of claim 36, wherein the power situationcomprises a power level of a battery falling below a predeterminedthreshold and wherein changing an image display property includesdecreasing at least one of the video color quality, screen resolution,and screen refresh rate.
 43. The computer-implemented method of claim36, wherein the power situation comprises a power level of a batterymeeting or exceeding a predetermined threshold and wherein changing animage display property includes increasing at least one of the videocolor quality, screen resolution, and screen refresh rate.